Abstract: In order to solve the problem of low flame retarding efficiency and poor smoke suppression effect of magnesium hydroxide (MH), nano-sized molybdenum oxide doped magnesium hydroxide (MO@MH) was prepared by one-step hydrothermal method. The flame retarding and smoke suppression efficiency of MH was improved by the Lewis acid catalytic cross-linking effect of nano-sized molybdenum oxide. XRD, SEM, TEM and element distribution results showed that MoO₃ was deposited in magnesium hydroxide (MH) layers with thickness of 10~20 nm in the form of particles less than 10 nm. The MH layers were further stacked to form flower spheres with size of 20~30 μm. The results of flame-retardant tests showed that the flame retardant and smoke suppression efficiency of MO@MH fPVC was obviously better than that of MH. The peak heat release rate and peak smoke production rate of MO@MH-1/fPVC composite were 33.64% and 75.16% lower than those of MH/fPVC composite, respectively. MO@MH/fPVC composites also passed V0 rate in the vertical tests. The results of char residue analysis showed that the addition of MO@MH can produce the outer char residue mainly composed of MgO and MgMoO₄, and the inner char residue mainly composed of graphitized carbon, MgO and MgMo₂O₇. The quality, density and integrity of the char residue of MO@MH/fPVC composites were significantly improved compared with that of MH/fPVC composite. The + 6 Mo element participated in the charring process of fPVC matrix through oxidation-reduction reactions to form +4 Mo compounds. The mechanical properties test results showed that MO@MH had better toughening effect on fPVC matrix than MH, and the impact strength of MO@MH-1/fPVC composite was increased by 32.34% compared with the MH/fPVC composite. The main reason was the poor interface compatibility between MO@MH and fPVC matrix and the existence of interface defects caused by complex structure.